This invention relates to the adjustment, i.e., increase or decrease, of the entropy (randomness) of digital information. More particularly, the invention relates to a method and apparatus which employs entropy adjustment in connection with the compression of randomized digital data, such as graphical images, video signals, digital datasets, including computer programs, databases and the like, whether or not a prior compression technique has been applied to the information.
Entropy is the measure of randomness of information. In the context of graphical images, entropy is a general measure of image "bumpiness"--the greater the bumpiness, the higher the entropy and the greater the amount of information that must be transmitted or stored. It is desirable to reduce the amount of information transmitted or stored, particularly image information, because spectrum and storage represent wasteful use of resources.
To understand how this "bumpiness" comes about in image data, consider a picture composed of just red and green "planes." If the red and green planes were each constant across the image, but of different levels, then in principle it would require only two numbers to specify the two (constant) levels. However, a combination plane that is derived from such an image would be composed of an interlaced checkerboard of constant red and constant green values, but with the red and green values at different levels. The combination image would thus have a strong component at a high spatial frequency, or high entropy.
In the past, it has been known to apply entropy reduction techniques to digital information in connection with data compression in order to minimize the information storage/transmission requirement. In the past, entropy has often been assumed to increase upon compression. Further study, however, shows that compression and entropy reduction techniques can be used together beneficially to optimize compression.